How the ASSYST Service Interval System Works
Modern Mercedes-Benz vehicles (approximately 2000 onward) use an ASSYST (Advanced Service System) oil life monitoring system rather than fixed mileage intervals. ASSYST calculates remaining oil life based on engine speed, load, temperature cycles, and time — not mileage alone. A car driven mostly at freeway speeds in mild temperatures will have longer ASSYST intervals than the same car driven in heavy stop-and-go traffic with lots of cold starts. The system counts down from 100% to 0%, at which point it triggers a service reminder.
The alternating Service A / Service B designation just tracks whether the next service is a minor or major interval. The system starts at Service A, then advances to Service B, then back to Service A, and so on. Service A typically occurs around 10,000 miles or one year; Service B approximately one year after that.
What Service A Includes
| Service A Item | Notes |
|---|---|
| Engine oil and filter replacement | Correct MB-approved spec oil required (see oil spec guide) |
| All fluid levels topped off | Coolant, washer fluid, power steering |
| Brake inspection | Visual measurement of pad thickness front and rear |
| Tire inflation check | Adjust to placard specification |
| Tire rotation (if needed) | Some models; check staggered fitment before rotating |
| Service indicator reset | Requires XENTRY or compatible MB reset tool |
What Service B Includes
| Service B Item | Notes |
|---|---|
| Everything in Service A | Oil, filter, fluids, inspection |
| Brake fluid replacement | Every Service B (approximately every 2 years); glycol-based fluid absorbs moisture |
| Cabin air filter replacement | More frequently in Southern California dust conditions |
| Spark plugs (on schedule) | Only when the spark plug interval aligns with Service B; not every B service |
| Full system inspection | All major systems evaluated; notes on upcoming maintenance needs |
| Service indicator reset | B designation cleared, system advances to next A interval |
Dealer vs. Independent Shop: The Real Cost Comparison
A Service A at a Mercedes-Benz dealer in the Los Angeles area typically runs $280–$450. A Service A at an independent Mercedes specialist using the same oil specification, the same filter, and the same service procedures runs $120–$200. Service B at a dealer runs $600–$950. The same Service B at an independent shop: $280–$450. The difference is dealer overhead, the dealership service advisor commission structure, and marketing costs — not the quality of the work or the parts.
Magnuson-Moss Act: Under federal law, a manufacturer cannot void your factory warranty because you used an independent shop for maintenance, provided the service was performed correctly with appropriate parts and fluids. Keep all receipts and document the fluid specifications used. Mercedes cannot legally require dealer service as a warranty condition for the base factory warranty.
What to Ask Your Shop
When booking a Service A or B at an independent shop, confirm three things: what oil specification they're using (should be MB 229.5 or 229.51 depending on your engine — see the oil spec guide), whether they have the capability to reset the Mercedes service indicator correctly (requires a Mercedes-specific tool, not a generic OBD-II scanner), and whether brake fluid testing is included in Service B (it should be; a refractometer test verifies the glycol content hasn't degraded below spec before simply replacing it on schedule).
An independent Mercedes shop that answers these questions confidently is performing the same service as the dealer. One that can't confirm the oil specification or says they'll "just use a good full synthetic" is not.